Detect lightweight java language server

[rzgry]

Fixes #12

Detects if java ls started in lightweight mode and prompts user to switch to standard. The user ends up getting a second prompt from vscode-java to ask if they are sure.

[datho7561]

This is pretty helpful for switching to the full Java language server from the lightweight mode. Before the user responds to the dialog box, NPEs will be generated, since the client program doesn't wait for the user to respond before starting lsp4mp. If 'no' is selected in the first dialog, then the microprofile server is left running, which means NPE are still generated.

[angelozerr]

@fbricon could you give us feedback please about this fix.

[fbricon]

See microsoft/vscode-java-debug@20cd68c for reference

[rzgry]

I agree with trying to avoid starting up lsp4mp if the java language server is in lightweight mode.

I opened an issue redhat-developer/vscode-java#1571 to try and get some clarifications about the best way to go about implementing this. I can detect the current server mode on start up. But since vscode-java can start in lightweight and switch over to standard after activation, if we detect lightweight at start up it can display a warning to switch to standard even though vscode-java is in the process of switching over to Standard which i dont think makes for a good UX.

[rzgry]

After some discussion in this issue: redhat-developer/vscode-java#1571 It seems that it can be problematic to check the java language server mode immediately on extension activation. This is because when you import a new project vscode-java starts off in lightweight mode and prompts the user to switch to standard.

The flow for importing a new java project seems to be:
Someone imports a new Java project. -> Java language server starts in Lightweight. They are then prompted to import the project. If they click yes -> Java language server will switch to Hybrid as it starts up the Standard server, and then to Standard once the standard LS is ready.

So for new Java projects, if we check the mode immediately on extension activation it will return lightweight, even though the user could be in the process of switching to standard mode using the prompt from vscode. Which means we could end up displaying an unnecessary warning message.

For an example:

I click yes to import the project and switch to standard. But since immediately at activation vscode-java returns Lightweight we end up with a warning message from vscode-microprofile to switch to standard.

It seems for all the other Java extensions, they detect server mode only when java features are needed instead of immediately on extension activation.

My thoughts are that would could do something like only check the Java language server mode after a user has opened a file or something similar.

Any thoughts @fbricon @angelozerr @datho7561 ?

[rzgry]

Update the PR to only start the MicroProfile language server once the java language server is in hybrid mode.

After testing redhat-developer/vscode-java#1581 it fixed the problem when a new importing a project for the most part.

If someone selects yes to import a new project before vscode-java is done activating, they will no longer receive a second prompt while the standard server is in the process of launching.

You can still get two prompts when importing a project if the user has not selected Yes to import the project by the time vscode-java has finished activating. But i think this is acceptable?

Ex:

[fbricon]

I think we can start that way.

[rzgry]

Updated the options for the prompt to switch to Standard to be Yes and Later to match vscode-java.

[datho7561]

Works well for me. The behaviour is pretty intuitive.